330 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



first premolar (dp^) is about as large as in the adult 

 Princeton Mus. 10009. The large alveolus of the 

 canine appears to leave no room for the formation of 



Stage with milk teeth and one permanent molar in 

 use: This stage is represented by a maxilla (Am. Mus. 

 1565, PL LIX, figs. 282, 283), probably referable to 

 Palaeosyops leidyi, and by a lower jaw (No. 

 12197, level C 2) belonging to another indi- 

 vidual of the same size. In these specimens 

 the length of the ramus is estimated at 300 

 millimeters. In the upper jaw two upper 

 milk incisors and the milk canines are in 

 place; dp^ is a simple, conical tooth, smaller 

 than its successor p^; dp^ exhibits two ex- 

 ternal crescents, a parastyle and mesostyle, 

 and two internal cones, but the crown is 

 oblong and not molariform; dp' exhibits the 

 same elements more fullj'' developed, the 

 crown small and more quadrate in form, 

 small conules, submolarif orm ; dp* is entirely 

 molariform, with protoconules and meta- 

 conules and fully quadrate contours; m' is 

 also in use. 



The juvenile jaw, Am. Mus. 12197, belong- 

 ing to an animal of exactly the same size as 

 that to which the above-described maxilla 

 pertained, exhibits the following characters: 

 Dp2 is of small size but similar in form and 

 not more progressive than its permanent 

 successor p^; dps and dp4 are in every respect 

 fully molariform. 



Leidy's type of Palaeosyops Tiumilis: The 

 single tooth from the "Dry Creek beds," 

 Bridger formation, figured in Leidy's memoir 

 of 1873 (1873.1, pi. 24, fig. 8) is the third 

 superior milk molar (dp') of the left side of 

 the jaw, belonging to an animal slightly 

 inferior in size to P. leidyi. Its agreement 

 in all essentials with dp' of the milk dentition, 

 Am. Mus. 1565, above described, makes it 

 clearly referable to the genus Palaeosyops, 

 but geologic evidence for this reference is 

 lacking, as its exact level is unrecorded; it 

 might therefore belong to P. major, P. leidyi, 

 or P. rohustus. Hence it seems best to regard 

 P. Tiumilis as an indeterminate species. 



Conclusions. — (1) There is evidence in 

 Palaeosyops of the presence of at least two 

 upper milk incisors, one milk canine, and 

 Figure 280. — Lower jaws of Palaeosyops leidyi three milk premolars on each side above, or 



One-fourth natural size. Ai, Am. Mus. 1546 (reversed); Bridger Basin, Wyo.; side view; condyle 10 rlppirliinnci tpptli nhnvo nil +ncrot>iAr' (9^ 



restored from Am. Mus. 6103, angle from Am. Mus. 1622. A,, The same, anterior view of section -^^ aeCmUOUS tCetU aDOVe ail tOgCtUer, {Z) 



through line b. Ai, The same, anterior view of section through line c, with coronoid and condyle, the first Upper and loWCr premolars (Pt) are 

 B, Am. Mus. 16C4; Henrys Fork, Bridger Basin; upper Bridger; coronoid and chin supplied from . . i i • i • i 



Am. Mus. 1585, incisors and canine from Am. Mus. 1544. C, Am. Mus. 1644 (type); Henrys Simple, COniCal tCCth, whlch are retained 



Fork, Bridger Basin; Bridger, level probably upper C or D. i. Abnormal, extra premolar. • .1 rl 1 + 



a permanent successor, or p'. The evidence is still 

 insufficient, however. In the Oligocene titanotheres 

 p' may also be a persistent milk tooth (dp'), as it is in 

 recent horses. 



dentition — that is, they 

 are probably without predecessors, or milk teeth; 

 (3) the second lower deciduous premolar (dp2) 

 resembles in form its successor p2 except that the 

 posterior lobe is better developed; (4) in correlation 



